Foundations for the support of equipment and pipelines used in the oil and gas industry can be supported by piles having helical blades which are screwed into the ground in a manner that is similar to a "self tapping" wood or metal screw. A positive displacement hydraulic motor whose output shaft is coupled to the top of the pile can be employed to turn it and thereby advance the pile into the ground. In a typical installation, piles are placed on opposite sides of the pipeline, and a suitable bracket that is connected to the upper end portions of the piles and to the pipeline provides a support or foundation therefore. Such installations typically are made at spaced points along the pipeline to provide adequate support, as needed.
The level of torque that is required to turn the screw pile is indicative of the strength of the soil, and can be used to predict the capacity of the pile. Low installation torque indicates a weak soil and low pile capacity, whereas high installation torque indicates a relatively strong soil and greater pile capacity. Where the required installation torque can be accurately measured, the approximate holding capacity of a screw pile can be reliably predicted.
A torque indicator that has been used in the past includes a pair of flange or disc members which provide a coupling mechanism that transmits torque between upper and lower sections of the motor drive shaft. The disc members are formed with a plurality of axially aligned pairs of holes, each of which is arranged to receive a metal pin having a known shear value, for example 500 ft. lbs. Most indicators of this type will accept from 1 to about 20 pins, and possibly more. When the operator desires that the drive shaft be disabled at a torque level of about 3,000 Ft. lbs., for example, a total of 6 shear pins are mounted in the holes in the disc members. Then the screw pile is torqued down into the ground until the pins shear off, which disables the motor drive shaft at that point.
If the screw pile that is being driven is not fully down when the pins shear, then a larger number of shear pins must be loaded into the disc members to provide a higher torque level at which the drive shaft will be disabled. In any event, a selected number of new pins must be used in order to drive another screw pile during continued foundation forming operations. Thus the necessity to repeatedly remove broken shear pins and replace them with new ones results in considerable down time which slows the progress of the work considerably, and thus increases the overall cost of pile foundation construction in an undesirable manner.
An object of the present invention is to provide a new and improved torque indicator system which accurately monitors screw pile installation torque while eliminating the disadvantages noted above.
Another object of the present invention is to provide a new and improved indicator system which provides a measurement of the pressure drop across hydraulic or pneumatic components.